Molecular evidence for an African origin of the Hawaiian endemic Hesperomannia (Asteraceae)

Identification of the progenitors of plants endemic to oceanic islands ofte n is complicated by extreme morphological divergence between island and con tinental taxa. This is especially true for the Hawaiian Islands, which are 3,900 lan from any continental source. We examine the origin of Hesperomann ia, a genus of three species endemic to Hawaii that always have been placed in the tribe Mutisieae of the sunflower family. Phylogenetic analyses of r epresentatives from all tribes in this family using the chloroplast gene nd hF (where ndhF is the ND5 protein of chloroplast NADH dehydrogenase) indica te that Hesperomannia belongs to the tribe Vernonieae. Phylogenetic compari sons within the Vernonieae using sequences of both ndhF and the internal tr anscribed spacer regions of nuclear ribosomal DNA reveal that Hesperomannia is sister to African species of Vernonia. Long-distance dispersal northeas tward from Africa to southeast Asia and across the many Pacific Ocean islan d chains is the most likely explanation for this unusual biogeographic conn ection. The 17- to 26-million-year divergence time between African Vernonia and Hesperomannia estimated by the DNA sequences predates the age of the e ight existing Hawaiian Islands. These estimates are consistent with an hypo thesis that the progenitor of Hesperomannia arrived at one of the low islan ds of the Hawaiian-Emperor chain between the late Oligocene and mid-Miocene when these islands were above sea level. Subsequent to its arrival the sou theast Pacific island chains served as steppingstones for dispersal to the existing Hawaiian Islands.